This invention relates to a transmission apparatus for a vehicle having an input shaft connected to an internal combustion engine, an output shaft connected to a driving wheel of the vehicle, and plural gear trains of different change speed stages interposed between the two shafts through respective clutches.
There has been known an arrangement, as shown in FIG. 1 for instance, of a transmission apparatus having four gear trains d-R, d-1, d-2, d-3 for a one-reverse stage and three-forward stages interposed between an input shaft a and an output shaft b through respective clutches c-1, c-2, c-3. The clutch c-2 for the second speed gear train for the forward middle speed stage is arranged to be a common clutch used also as a clutch for the reverse gear train d-R so that these two gear trains d-R, d-2 may be interposed selectively between the input and the output shafts a, b through the common clutch c-2 and a selection mechanism e provided separately therefrom. Thus, an intention of shortening of the axial size of the transmission apparatus is achieved by omitting a clutch for exclusive use for the backward driving. It becomes possible to mount the resultant transmission apparatus on a small-sized horizontal front engine-front drive type motorcar which restricts the axial size of a transmission apparatus to be mounted thereon. Referring to the same FIGURE, P denotes a gear for parking.
To thus decrease the number of clutches by omitting the clutch for exclusive use for the backward driving is advantageous not only in lightening the weight of the apparatus but also in decreasing in a total amount of loss torque caused by a clutch dragging phenomenon. However, the foregoing apparatus is inconvenient in that when the selection mechanism e is changed over to the reverse driving side and the common clutch c-2 is engaged to effect the backward driving, a friction plate on the input side of the clutch c-3 for the 3rd speed gear train of a forward high speed stage is rotated at a high speed in accordance with rotation of the input shaft a through the 3rd speed gear train d-3, and a relative rotation speed thereof through the 3rd speed gear train d-3, and a relative rotation speed thereof in relation to a friction plate on the output side of the clutch c-3 rotated together with the rotation of the output shaft b becomes very high, and thereby a loss torque caused by the dragging phenomenon is increased.
This loss torque problem should be taken into consideration also in such a case that the number of forward change speed stages in a transmission apparatus is increased to 4 stages or 5 stages and a common use of clutches for those forward gear trains is intended. Also in this case, consideration has to be taken on the influence over driveability by a time lag caused when the gear trains are selectively changed over by a selector.